It is generally understood that, for a polymer blend to be useful as a coating material, outstanding performances with respect to several criteria including optical behaviour (e.g. gloss and weatherability), hardness, abrasion resistance, no dirtiness, etc. are required.
Vinylidene fluoride (VDF) polymers, possessing unique properties such as exceptional weathering resistance, good abrasion resistance, high mechanical strength and toughness, etc., have been used as base material for coatings, and more particularly for highly weatherable architectural coatings for years. For improving adhesion to substrates, pigment dispersion ability and increasing coating gloss, miscible VDF polymer blends with (meth)acrylic resins have been developed. As optical behaviour of a coating, including e.g. gloss, typically requires coating matrix continuity, thermodynamically miscible blends are preferred, especially for exterior architectural finish applications. Said miscibility also allows the final coating to maximize coating weatherability in long term exterior service.
In view of the above, blends of VDF polymers and (meth)acrylic resin at around a 70:30 weight ratio have been proven to provide optimum material performance with respect to criteria such as adhesion, toughness and optical clarity.
Nevertheless, there is still a need in the art for improving appearance of coatings obtained from VDF polymer compositions, including improving their gloss and stain repellence.
This having said, it is worth mentioning that document WO 2008/065164 (SOLVAY SOLEXIS S.P.A.) May 6, 2008 discloses compositions comprising VDF polymers and certain block copolymers comprising a PFPE block and a further block derived from polyaddition polymerization of ethylenically unsaturated monomers, e.g. tetrafluoroethylene. Nevertheless, such block copolymers are merely used as lubricating additives, conferring to the VDF polymer an improved processability, in particular lower pressure and/or lower torque in extrusion. Nowhere in this document, is mention made of the suitability of these additives in coating compositions.